Differential Equations

[Julian]

I think I just figured out what I did wrong.

Because of that x^2 in front of the y'', it's not in 'standard form', so I guess I was supposed to divide everything by x^2 before starting out? >_>

I think that's it... don't really feel like actually trying the problem again tho, wooo spring break!

[Woozie]

Suriam: the Zill book I have is the seventh edition. It's actually like 400+ pages. It seems so much smaller though. But I guess you should really just grab the cheapest edition if your library doesn't have the book.

Julian: I'll probably work on this problem sometime tonight or tomorrow. Since you don't seem to need it anymore, I'm not in a hurry to do it.

[Kaylia]

Think you could be my study buddy for electromagnetism? lol This stuff is kicking my butt, ugh I hate math so much, but at the same time this stuff is so interesting lol

You can always send me a pm here or on AIM if you have a physics question. I like answering that kind of stuff, if I can, that's it.


And if you think electromagnetism kick your butt, wait till fluid dynamics. It's strangely similar, but I don't think I understood anything in the 2nd half of the semester,

[mdkuser]

(x^2)y'' + 2xy' - 2y = 6x^-2 + 3x, x>0

Anyone know how to solve this? for a general solution.

This is not a HW question, I'm studying for an exam today, and this is the only type of problem that I wasn't able to solve.

So steps to the solution so I can understand it would be greatly appreciated, thanks.

edit: So far I got, using the Cauchy-Euler thing, I got the answer to the homogeneous part, c1x^-2 + c2x, but for finding a particular solution.... uhhhhh >.>

answer: y=-2*ln(x)*x^(-2)+x*ln(x) (double checked)

There is a method to find a solution once you have solutions for the homogenous equation, idk what the english term is , we call it the "variable constant method.." basically you look for a solution of type

y=c1x^-2 + c2x with C1 and C2 not constant... would be a bit long to explain if you have never seen it before lol.

The term x^2 if front of y'' means x=0 will be a problem so you might want to put ln|x| instead when x<0.

[Suiram]

Thanks Woozie, I'll look into that.

[Julian]

answer: y=-2*ln(x)*x^(-2)+x*ln(x) (double checked)

There is a method to find a solution once you have solutions for the homogenous equation, idk what the english term is , we call it the "variable constant method.." basically you look for a solution of type

y=c1x^-2 + c2x with C1 and C2 not constant... would be a bit long to explain if you have never seen it before lol.

The term x^2 if front of y'' means x=0 will be a problem so you might want to put ln|x| instead when x<0.

Yes that's the answer, and the question also says x>0 so don't have to worry about that. Not sure I know what you're trying to explain. I think I'll try this problem again tomorrow to see if the x^2 really was the problem <.<

[zoobernut]

who cares if you can do math, it's how you apply it!
(I'm applied math major lol)

Sorry Woozie I am an applied math major too.

Also my HS had Calc AB and BC as well as many other AP classes like physics chem, bio, and all the other ones.

It was really nice.

I haven't started my math classes yet, taking all the computer science first.

[Woozie]

Sorry Woozie I am an applied math major too.

You too, Zoobernut? I thought we were friends

[zoobernut]

You too, Zoobernut? I thought we were friends

I could change to theoretical math at any moment, or maybe statistics. Whatever is best for the job I already have.


Don't worry I will still be your friend.

[Demosthenes11]

if it helps im thinking of swapping to chinese major (would fun to be the lone white guy). math is boring anymore (in complex planes atm)

[Kaylia]

Do a physics major, and you will start appreciating maths. They are often boring to people who can't see their use.

[Neosutra]

This thread made me nostalgic, broke out the DE book for some pleasure reading..

I probably shouldnt admit that >.>

[SDSD]

if it helps im thinking of swapping to chinese major (would fun to be the lone white guy). math is boring anymore (in complex planes atm)

Why not just do the double? (I can answer that actually. It's horrible.) And anything with complex numbers or properties makes me scream. It's all about real analysis.

@Woozie What about a pure math major, who does applied math research in biology?

[Woozie]

If you're doing applied math in school as research, fine. But if you're doing that as a career, you're one of them. ONE OF THEM!!!!!!!!!

Edit: I agree with Real Analysis being awesome. I'm going to write my thesis on something related. Every other pure math major here seems be going towards group theory.

[Mojo]

I'm an applied Math major. I'm doing it because it'll make more money, although I do enjoy pure math much more.

[Woozie]

Sell out D:

Edit: I guess I'm a sell out too. I wanted to go into theoretical physics until I found out how hard it is for theoretical physicists, and how much easier it is for applied physicists (and how much more they make). Now (assuming I go into physics and not math. I'm still not 100% sure on that yet) I'm planning to go into applied D:

But if I go into math, it will probably be theoretical since they have it somewhat easier than theoretical physicists. And plus I'm already working on my masters in pure math, so I may as well stick to pure math for my PhD if I go the math route.